This invention relates to preparation of bisphenols, particularly bisphenols having a carbon atom having bonded thereto an aliphatic group and at least three aromatic groups, at least two of which aromatic groups each have at least one phenolic group, hereinafter referred to as triaromatic bisphenols. Bisphenols are the building block molecules for such materials as polycarbonates, epoxy resins, polysulfones, polyarylates and the like. Bisphenols in which the phenolic rings are joined together through a single bridging carbon are usually manufactured by condensing two moles of phenol with an aldehyde or a ketone in the presence of an acid catalyst. Bisphenol A is the most commonly used bisphenol and is made from the reaction of acetone with phenol. Because it must be performed under mild temperature conditions (50-70.degree. C.) to minimize the formation of undesirable coproducts, it is a slow reaction. Other bisphenols are employed to impart specific properties to the above resins. Some of these properties are, for example, toughness, strength, better thermal properties and solvent resistance. Bisphenol AP, the bisphenol of phenol and acetophenone (bis-1,1-(4-hydroxyphenyl)-1-phenylethane), is known to improve the thermal properties of polycarbonates, polyarylates and epoxy resins over similar materials made from bisphenol A.
The condensation of phenol with acetophenone, however, is very slow. Even with zinc chloride as a catalyst, the reaction requires two days to complete (U.S. Pat. No. 4,467,122). Then an extended work-up must be performed to remove as much residual zinc salts as possible. With HCl as the catalyst, the reaction requires 10-14 days. These process limitations, along with the lack of commercially significant quantities of acetophenone, have hindered the development of useful applications for Bisphenol AP. A more facile process should allow wider use of this valuable monomer.
In order to achieve the high molecular weights required to produce the desired thermal and mechanical properties, the bisphenol starting materials for such thermoplastics as polycarbonates and polyarylates preferably have the constituent phenol groups substituted in the para position in greater than 98% selectivity. Although most of the ortho-substituted material can be separated by crystallization, it is most desirable for good process economics to minimize the product containing any ortho isomer. In one reference, J. American Chemical Society, 76, 4547(1954)], 1-chloroethylbenzene is reported to react with phenol to give a mixture of isomers of 1-(hydroxyphenyl)-1-phenylethane having the hydroxy group of the phenyl group in the ortho and para position in a mole ratio of 55 ortho to 45 para position.
It would be desirable to prepare triaromatic bisphenols more quickly than is typical for condensations of acetophenone with phenols and to prepare them such that there is a high selectivity for the para isomer. Bishydroxyphenyl compounds, including triaromatic bisphenols, are preferably in the para isomer form (having the hydroxy group on the phenyl ring para to the attachment of the phenyl ring to the carbon atom to which the other phenyl group(s) are attached) because such isomers result in high polymers with desirable properties of high molecular weight, impact strength, modulus and the like.